The United States is halting some shipments of weapons previously promised to Ukraine after a Pentagon review determined that US stockpiles have declined too much.

Malcolm Chalmers, deputy director-general of the Royal United Services Institute military think tank, told CBS News in March that about 20% of Ukraine's military hardware is supplied by the U.S., with 25% provided by Europe and the rest of the world, and 55% produced in Ukraine.

The White House cited Pentagon concerns that some American arms stockpiles were dwindling too low. Among the affected weapons were air defense systems, bombs, missiles and artillery rounds.